小编let*_*ian的帖子

以下是我在ruby中实现的shuffle算法:

def shuffle03!(arr)
    len = arr.length
    for i in 0..len-1
        index1 = Random.rand(0..len-1)
        index2 = Random.rand(0..len-1)
        arr[index1], arr[index2] = arr[index2], arr[index1]
    end
end

我通过推算测试了这个算法:

class ShuffleTest
    def initialize(seed)
        len = seed.length
        @count = {}
        for i in 0..len-1
            @count[seed[i]] = Array.new(len, 0)
        end
    end
    def test(arr)
        for i in 0...arr.length
            @count[arr[i]][i] += 1
        end
    end
    def show_count
        return @count
    end
end


def shuffle03!(arr)
    len = arr.length
    for i in 0..len-1
        index1 = Random.rand(0..len-1)
        index2 = Random.rand(0..len-1)
        arr[index1], arr[index2] = arr[index2], …

在下面的代码nameRef.get()是null,之后name = null和System.gc().

import java.lang.ref.WeakReference;

public class Main {

    public static void main(String[] args) {
        String name = new String("ltt");

        WeakReference<String> nameRef = new WeakReference<>(name);    
        System.out.println(nameRef.get()); // ltt

        name = null;
        System.gc();

        System.out.println(nameRef.get());  // null
    }    
}

WeakHashMap基于WeakReference.最后,我认为map.size()将是0.事实上,它是1.

import java.util.WeakHashMap;

public class Main2 {

    public static void main(String[] args) {
        String name = new String("ltt");
        WeakHashMap<String, Integer> map = new WeakHashMap<>();
        map.put(name, 18);
        System.out.println(map.size()); // 1

        name = null;
        System.gc();

        System.out.println(map.size());  // …

然后返回指定的Promise给出以下代码段：

function get(url) {
  return new Promise(function(resolve, reject) {
    var req = new XMLHttpRequest();
    req.open('GET', url);

    req.onload = function() {
      if (req.status == 200) {
        resolve(req.response);
      }
      else {
        reject(Error(req.statusText));
      }
    };
    req.onerror = function() {
      reject(Error("Network Error"));
    };
    req.send();
  });
}

该功能可以如下使用：

get('story.json').then(function(response) {
  console.log("Success!", response);
}, function(error) {
  console.error("Failed!", error);
});

我想使用Promise来加载多个网址，例如

get('a.json').get('b.json')
// or get('a.json').then().get('b.json')

我已经以其他方式实现了它。但是据我了解，Promise无法完成这项工作。真的吗

加

实际上，我实现了一个类似的库，可帮助在浏览器中执行动态脚本：

Loader = (function() {

  var load_cursor = 0;
  var load_queue;

  var loadFinished = function() {
    load_cursor ++;
    if …

Java 将时间戳 -923130000 和 -923130001 解析为 LocalDateTime 失败。两个结果之间的秒数是3599，太奇怪了。

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;

public class TestLocalDateTime {

    public static void main(String[] args) {
        System.out.println("-923130000: " + toLocalDateTime(-923130000L));
        System.out.println("-923130001: " + toLocalDateTime(-923130001L));

        System.out.println(ChronoUnit.SECONDS.between(toLocalDateTime(-923130000L), toLocalDateTime(-923130001L)));
    }

    private static LocalDateTime toLocalDateTime(Long timestamp) {
        return LocalDateTime.ofInstant(Instant.ofEpochSecond(timestamp), ZoneId.systemDefault());
    }

}

输出：

-923130000: 1940-09-30T23:00
-923130001: 1940-09-30T23:59:59
3599

爪哇版：

$ java -version
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

代码在 macOS 上执行。